This invention relates to power amplifier circuits. More particularly, this invention relates to circuitry of the above type used to increase the power level of an information signal by drawing power from an A.C. supply.
Power amplification circuits are known which function to increase the power level of an information signal to a level required to operate associated utilization devices by drawing power from the A.C. mains. Such circuits have a wide variety of uses, and special circuits have been developed for many particular applications, including servo control, cathode ray tube deflection, audio signal amplification, electric motor drive and other comparable uses. Known power amplifiers typically require a large power transformer in order to convert the A.C. voltage supplied by the mains to a suitable D.C. voltage. Such transformers are expensive to manufacture, are relatively large in size and weight, and generate significant amounts of useless heat which, unless dissipated, adversely affect the performance of other active and passive electrical circuit elements used in amplifier circuits. Power amplifier circuits employing a large power transformer suffer accordingly from the disadvantages inherrent in the use of such a large transformer.
Ideally, any power amplifier circuit should be relatively insensitive to component parametric changes in order to provide stable operation of the circuit. Further, a power amplifier circuit should ideally convert the electrical A.C. power to D.C. power with a minimum of heat generation to avoid parametric changes in the remaining circuit components. In addition, a power amplifier circuit should be compatible with a wide variety of loads, such as complex reactance loads, loads with characteristics which change with frequency, and regenerative loads (those which briefly supply power to the amplifier circuit), so that the performance of the amplifier circuit is not affected by the nature of the load. Moreover, the operating band width of a power amplifier circuit should be compatible with the anticipated range of frequencies to be amplified and, ideally, to be suitable for a wide variety of uses the band width should extend from about 0 HZ to several thousand KHZ. Efforts to design a power amplifier circuit approaching these characteristics have not been successful to date.